1. Field of the Invention
This invention relates to computer systems, and more particularly, to error checking and correction in memory subsystems.
2. Description of the Related Art
Many high-end computer systems include within their memory subsystem a feature known as ‘ECC’. ECC (error correcting codes, or alternatively, error checking and correction) is used to detect corrupted data in memory, and if possible, to correct the corrupted data. Data in memory may become corrupted by various sources, such as natural background radiation, electrical noise, failing components, and so forth.
ECC subsystems work by using the desired memory contents as a basis for computing additional bits to form the error correcting codes. Both the data and the bits making up the ECC are stored in memory. In some ECC-compliant systems, the bits comprising the ECC's may be stored separately from the data in which they protect (e.g., as in some RAID systems). In other ECC-compliant computer systems, special memory devices are used for storing data and the bits comprising the ECC. These memory devices require additional storage space (12.5% in one type) for storing the ECC's along with the protected data. The additional storage space in turn requires additional interconnections (i.e. connectors and circuit traces) to convey the additional bits between the memory controller and the memory. ECC memory components are used primarily in high-end computer systems, and thus their use has not become widespread enough to attain economies of scale. Thus, implementation of ECC in a memory subsystem may require significant additional cost.
In addition to the cost factor, implementation of ECC memory in some computer systems may be impractical. For example, physical space for implementing extra interconnections and storage space is significantly limited (if available at all) in laptop computer systems. Space may also be limited in some desktop computer systems as well. Thus it may not be possible to use ECC-compliant components in such system even if it is otherwise desirable to do so.